This invention relates to an improvement of a device which manufactures glass fibers by utilization of centrifugal force, and is intended to form glass fibers high in quality which form glass wool, and to economically use thermal energy.
In a device for manufacturing glas wool by utilization of centrifugal force, molten glass is introduced to the inner surface of the surrounding wall of a rotor which is rotated at high speed, for instance 3000 r.p.m., and is projected through a number of orifices in the surrounding wall of the rotor to form primary filaments. The primary filaments are attenuated into secondary filaments by the jet flame means. The secondary filaments thus formed are utilized to form glass wool.
In a device of this type, it can be observed that molten glass projected onto the outer surface of the surrounding wall of the rotor through a number of orifices in the surrounding wall are formed into transition cones of molten glass each having a small circular bottom corresponding to the opening area of the respective orifice on the outer surface of the wall. Primary filaments are formed at the tip of each transition cone of molten glass, and the primary filaments thus formed are advanced into jet flames which are adapted to subject the primary filaments to secondary attenuation, thus being formed into secondary filaments. In order to form the secondary filaments from the primary filaments, jet streams (such as jet flames or a jet air stream) the speed of which is high enough to cause secondary attenuation should not exist between the tip and the bottom of the transition cones of molten glass. The presence of such jet flames or jet air streams would break the transition cones of molten glass, and accordingly no primary filaments would be formed.
In the above-described device, the flow rate of molten glass passing through the many orifices in the rotor's wall is increased as the temperature of the molten glass is increased and accordingly the viscosity thereof is decreased. Of course, the flow rate is decreased as the temperature of the molten glass is decreased and accordingly the viscosity is increased. If the temperature of the molten glass is further decreased and accordingly the viscosity thereof is further increased, then the glass cannot pass through the orifices in the rotor's wall such that sometimes the supplied molten glass flows over the rotor. In this case, it is impossible to form desired fibers with the molten glass.
The viscosity of the molten glass is greatly affected by temperature. Therefore, maintaining at a predetermined temperature the molten glass passing through the orifices in the rotor's wall is essential in order that the flow rate of the molten glass projected through the orifices in the rotor's wall is maintained constant as are the diameters of primary filaments. Thus, fluctuation in the diameters of the glass fibers, or secondary filaments, which are formed by secondarily attenuating the primary filaments, is minimized. Accordingly, glass wool excellent in quality is provided. The temperature of molten glass passing through the orifices in the rotor's wall depends on the temperature of the rotor. In other words, as the temperature of a portion of the rotor, which includes the orifices, is increased, the temperature of molten glass passing through the orifices is increased; and as the temperature of the portion is decreased, the temperature of the molten glass is decreased.
On the other hand, in general, a high speed gas jet stream is employed as a means for secondarily attenuating the primary filament. Owing to the sucking effect of the gas jet stream, air is sucked through a circular hole C of an annular secondary attenuation member B as indicated by the arrow A in FIG. 1. The air passing through the circular hole C facilitates transformation of the molten glass projected through the orifices in the rotor's wall to transition cones of molten glass and then into primary filaments. However, the air thus sucked absorbs heat from the outer surface of the rotor and makes it difficult for molten glass to pass through the orifices. Therefore, maintaining the rotor at a predetermined high temperature by some means is essential to manufacture glass fibers by utilization of centrifugal force. For this purpose, a variety of means for heating the rotor have been proposed in the art. In a typical example of the means, a secondary attenuation jet device is provided, and a rotor heating burner is used to heat the rotor from outside and above. In the means, the flame is applied to the entire outer wall of the rotor including the upper end portion of the rotor. Therefore, in order to protect the aforementioned transition cones of molten glass used to form the primary filaments from breakage, the speed of the flame from the rotor heating burner should not be so high as to cause the secondary attenuation. Thus, a heating-only burner such as a radiation burner must be employed. Accordingly, an attenuating jet stream (high pressure and high temperature steam, in practice) device for subjecting the primary filaments to secondary attenuation must be additionally provided. Therefore, a glass wool spinning machine employing the means is intricate as a whole. Furthermore, as a high pressure and high temperature steam generating device must be used, thermal energy cannot be effectively utilized.
In another means for heating the rotor, a high frequency coil or an induction heater is provided outside of the rotor, so that the induction current of the coil is used to heat the rotor. However, this means is disadvantageous in the following respects. It is necessary to provide a high frequency generating device whose capacity is relatively large to heat the rotor. In addition, it is necessary to provide an electromagnetic shielding means around the glass wool forming machine with a high frequency generating device, to protect the operation from electromagnetic hazards. Therefore, the glass wool forming machine is rather intricate as a whole, and the operability of the machine is rather low.
In another means for heating the rotor, a burner is disposed inside of the rotor, to heat the rotor from inside. However, none of the means of this type is the same as that in the present invention in which a burner is set inside the upper annular flange of a rotor in such a manner that the flame from the rotor goes along the upper surface of the flange, or the upper and lower surfaces thereof, so that heat is transmitted to at least the corner where the upper annular flange and the surrounding wall of the rotor meet, and the direction of the flame is on the prolongation of the upper annular flange and in parallel with the surface thereof.
In the aforementioned conventional means in which a burner is used to heat the rotor from inside, the flame is applied only to the surrounding wall and the bottom of the rotor; that is, the flame is not applied directly to the corner where the upper annular flange and the surrounding wall of the rotor meet. In the conventional means for heating the rotor from inside with a burner, even if a flame is employed as the secondary attenuating jet stream, it is not intended to heat the rotor from outside with the attenuating flame. In order to positively form the primary filaments without breaking the transition cones of molten glass, the secondary attenuating burner is so positioned that the jet flame is not in contact with the rotor. The decrease of the temperature of the rotor outer surface which is caused by the air stream sucked in owing to the suction effect of the secondary attenuating jet stream as described above is compensated by allowing a large amount of flame from the inside burner to contact the bottom and surrounding wall (where heat is greatly radiated) of the rotor.
Since the upper portion of the rotor is substantially closed by the burner, heat is not so greatly radiated from the upper end portion of the rotor. Therefore, heat is supplied to the upper end portion of the rotor as follows. When a large quantity of flame inside the rotor flows from the bottom of the rotor towards the lower end portion of the surrounding wall of the rotor, it rises along the wall after contacting the bottom, thus reaching the inner surface of the upper flange extended from the upper edge of the rotor. As a result, heat is transmitted through the upper flange to the corner (the temperature increase of which is most difficult) where the upper flange and the surrounding wall of the rotor meet. In this manner, the upper end portion of the rotor is heated. Furthermore, a part of the large amount of heat which is applied to the rotor's surrounding wall by the large amount of inside flame is transmitted through the surrounding wall to the aforementioned corner, to heat the latter.
Accordingly, in the conventional means for heating the rotor from inside, it is necessary to supply a larger quantity of fuel gas to the burner positioned inside of the rotor. Thus, a particular device for supplying a large quantity of fuel gas to the narrow or small space in the rotor must be provided.
In each of the above-described three typical conventional means, in addition to the jet flame heat source for secondarily attenuating the primary filaments, a large capacity heat source for heating the rotor is required. Therefore, the conventional means cannot meet recent requirements that energy be economically used.